Thirteen students in three schools in Smithtown have been confirmed with the contagious bacterial infection.
Health officials in Suffolk County said Tuesday they had alerted area pediatricians and had given advice to school officials on how to control the outbreak.
Pertussis causes an uncontrollable, violent cough lasting several weeks or even months. It may begin with cold-like symptoms or a dry cough that progress to episodes of severe coughing. It is spread from person to person.
Officials say all of the Smithtown students had been immunized, helping to reduce the severity of their illness.
The three schools with ill children are St. James Elementary School, Tackan Elementary School and Nesaquake Middle School.